Telescopic ladders include multiple ladder sections, where the ladder is extendable or retractable for adjusting the height of the ladder by sliding the ladder sections relative to one another. Such telescopic ladders may employ a locking mechanism to securely fix the position of a first ladder section relative to a second ladder section, thereby preventing relative movement between the ladder sections, and conversely, to release the first ladder section and second ladder section from their fixed positions, thereby enabling relative movement between the ladder sections.
To date, various types of locking mechanisms for usage in association with telescopic columns or ladders have been proposed.
U.S. Patent Application Publication No. 2007/151195 to Huang, entitled “Telescopic column”, discloses a telescopic column that includes a cylinder and a post inserted in the cylinder partially. The post includes a ladder formed thereon. A mount is attached to the cylinder. A positioning element is installed on the mount pivotally. The positioning element includes a dent for engagement with the ladder during an attempt to insert the post into the cylinder and for disengagement from the ladder when the post is extended from the cylinder. A gear is installed on the amount rotationally. A handle is installed on the mount so as to provide pivotal in an active direction and in an idle direction opposite to the active direction. An extending element is installed on the handle movably. The extending element includes a detent for engagement with the gear in the active direction of the pivotal of the handle and for disengagement from the gear in the idle direction of the pivotal of the handle.
U.K. Patent Application No. GB 2,277,952 to Weston, entitled “Catch mechanism”, discloses a catch mechanism for mounting on the underside of a rung of a collapsible ladder, comprising a bolt, a spring acting to urge the bolt in a direction to lock two sections of one stile of the ladder to one another in the extended position of the sections and a release lever adapted to be pivotably mounted on the rung for retracting the bolt against the action of the spring. The release lever is pivotably connected to the bolt and the spring for urging the bolt in its locking direction acts between the bolt and the release lever.
U.S. Patent Application Publication No. 2008/000723 to Kieffer et al, entitled “Ergonomic extendable/retractable ladder”, discloses an extendable/retractable ladder assembly that includes a first column and a second column. The first column is nested in the second column. A first rung is coupled to and extends from the second column. A ladder assembly bracket includes a collar portion that extends about the second column, and a rung portion that extends from the collar portion into the first rung. The collar portion includes an outer surface and a recess formed in the outer surface, the recess being oriented and having a width to accommodate a portion of a hand grasping about the second column.
U.S. Pat. No. 5,924,523 to Krause, entitled “Adjustable ladder”, discloses an adjustable ladder that includes a base ladder and at least one extendable ladder movably fastened to the base ladder. The ladder extension can be locked by a locking bracket pivotally fastened on the extendable ladder. Guide rollers are arranged on the base ladder below a rung, and can be fastened by a first plug element serving as a mounting. The mounting is formed of a wire or rod-shaped blank. The mounting almost completely loops around the hollow section of the rung and is thereby bent in the direction of the rung axis. The mounting can be placed through a hollow axis or tube supporting the guide roller and fastened to a spar of the base ladder. The mounting extends through the spar and projects with a first end piece over the outer cheek or surface of the spar far enough that it can be fixed in the direction of the rung axis.
U.S. Pat. No. 6,189,654 to Bailey et al, entitled “Extension ladder”, discloses an extension ladder having a lower ladder section secured to an upper ladder section so that the upper ladder section can be extended relative to the lower ladder section using a ladder extension rope. Both ladder sections include a pair of spaced ladder stiles with rungs, and both ladder sections have the same width. A clutch mechanism extends between the ladder sections and is movable between a locked position, for maintaining the upper ladder section at a desired extension relative to the lower ladder section, and a released position allowing for relative movement of the ladder sections. A clutch locking mechanism biases the clutch mechanism into the locked position. The stiles of each ladder section has formations for securing the sections relative to one another and allowing the upper section to be extended and retracted relative to the lower ladder section.
Chinese Patent Application Publication No. CN 200971751Y to Fan Gang, entitled “Locking device for telescopic ladder”, discloses a locking device of a retractable ladder, which includes a lockpin mechanism. The lockpin mechanism includes a pin body, a locating hole and a spring. The locking device is characterized by an unlocking bevel and a locating bevel, which are fixed alternately on the pin body, on a cross piece of adjacent sections. An embedding cooperation part is mounted in correspondence with the unlocking bevel and the locating bevel. The unlocking bevel faces the head of the pin body and inclines to an adjacent section side with a corresponding embedding cooperation part. The facing direction of the locating bevel is the opposite of the unlocking bevel. When an upper one section or lower one section retracts from the current section, the embedding cooperation part of this section props against the unlocking bevel and pushes the pin body to shrink inside and get away from the locating hole, while at the same time, the other embedding cooperation part contacts with the locating bevel for locating.